Allowable ammonia for fish culture

A review of the published literature on effects of ammonia on fish indicates that un‐ionized ammonia alone is probably not the cause of gill hyperplasia, indicative of, or previously attributed to, chronic ammonia poisoning. The maximum safe concentration of un‐ionized ammonia is unknown, but in many cases it is not close to the 0.0125 mg/L value commonly accepted by fish culturists.